The present invention relates to a guide and seal assembly for a piston of a drowned piston type pump.
As is well-known, the pumps of the type specified hereinabove comprise at least a chamber in which a piston is reciprocated in order to suck into and supply from the said chamber a liquid; to obtain both the axial guide of the piston and the seal between the said chamber and the outside, assemblies are utilized which comprise one or more guide rings and sealing elements which are disposed in series in a suitable seat of the head of the pump and are apt to attain the two purposes mentioned hereinabove.
In the known seal assemblies a first annular seal member normally restrs on a corresponding seat of a first ring, which is kept in contact with a second seal member which is supported, in its turn, by a second ring. The said first ring is shaped and dimensioned in such a manner as to give origin, together with the surfaces of the piston and of the seat in which the assembly is housed, to two coaxial annular cavities which communicate with one another by means of one or more holes formed in the ring itself. Leading into the peripherically outmost cavity is a hole which connects the said cavity to a zone upstream of the suction valve of the pump, so as to suck from the said cavity the liquid which gathers in the cavity by passing through the first seal member and to convey it into the chamber in which the piston of the pump reciprocates.
According to a further technical solution of the problem, the said two rings are provided with parts which project both axially and radially, in order to also permit the first ring to directly rest on the second ring.
The seal assemblies constructed according to the two constructional solutions described hereinabove have some disadvantages. Both assemblies, but in particular the second assembly, are structurally rather complicated due to the shape of the first ring of the assembly; in fact, this ring, since it must give origin both to the two annular cavities which communicate with one another, and (in the case of the second technical solution) to the projecting parts mentioned hereinabove, is delimited by many surfaces having different diameters, and therefore its construction requires very precise mechanical operations and small working tolerances.
Furthermore, the assembly based on the first mentioned technical solution is not very satisfactory from the functional point of view, owing to the high force which the first ring discharges onto the second seal element, which force is generated by the considerable pressures which act onto the first element and are transmitted from this latter to the second element through the said forst ring.
Finally, in the assembly constructed in accordance with the second constructional solution some other difficulties arise in the construction of the seat of the assembly, since this seat is delimited by at least two cylindrical surfaces having different diameters.